One system for on-site storage of spent nuclear fuel utilizes a ventilated concrete horizontal storage module to passively store spent fuel assemblies sealed in a dry shielded canister containment vessel. The dry shielded canister containment vessel has an internal basket assembly with fuel storage locations similar to that of a fuel rack, each of which holds a spent fuel assembly. The loaded dry shielded canister is transferred from the planes spent fuel pool to a horizontal storage module located in an independent spent fuel storage installation using a transfer system that includes a transport trailer. The transfer system also includes an on-site transfer cask for containing the dry shielded canister containment vessel as it is being transferred from the fuel pool to the horizontal storage module. Once transferred to the storage installation, the dry shielded canister containment vessel is removed from the transfer cask and stored in the horizontal storage module until a monitored retrievable storage facility or a permanent storage facility is available.
As permanent storage facilities become available, it will be necessary for the dry shielded canister containment vessels to be transported from the on-site temporary storage facility to the off-site storage or disposal facility. Off-site transportation will use a transportation cask to contain the dry shielded canister vessel. Transportation of the spent nuclear fuel to off-site facilities will require that the dry shielded canister containment vessel and transportation cask be transported over public thoroughfares, such has highways, waterways, and railways.
During transportation, it is imperative that steps be taken to prevent leakage of radioactive material from the sealed cask and the containment vessel within the cask. Although the containment vessel and cask are shielded and sealed to prevent leakage, there is always a risk of damage to the cask and containment vessel caused by hypothetical accident impacts which might be encountered during transportation. Such impacts may be encountered during a collision involving the vehicle carrying the cask or possibly if the cask were to separate from the transportation vehicle during transportation.
One prior design for protecting the transportation cask and containment vessel from damage due to impacts includes "impact limiters" that include round, cylindrical elements carried on each end of the cylindrical transportation cask. Each impact limiter includes an annular region that encases a portion of one end of the cask. Such impact limiters include a foam, wood, or honeycomb material sandwiched between a rigid inner shell and a rigid outer shell. These impact limiters are designed to absorb energy upon impact and protect the transportation cask and containment vessel from damage.
Since the impact limiters must accompany the transportation cask over public thoroughfares, the space available for the impact limiters to pass through tunnels, bridges, and other highway, waterway, and railway features limits the overall size of impact limiters. The energy absorbing properties of the impact limiters with round, cylindrical elements often resulted in impact limiters that because of size limitations could not adequately protect a transportation cask that could carry a predefined amount of spent nuclear fuel. Therefore, in order to transport the predefined amount of spent nuclear fuel, additional trips would be necessary which increases the public's exposure to the fuel and the risk of an accidental incident. These previous impact limiters also generally employed one type of material, e.g., foam, wood, or honeycomb with directional crush properties in a given plane between the outer shell and the inner shell. Different densities of foam, wood, or honeycomb were used to soften the impact limiter in certain orientations in order to vary the crush characteristics. In addition, the impact absorbing material used in previous impact limiters was generally oriented radially between the inner and outer shell in order to take advantage of the properties of the material in its strongest direction.
Despite the existence of the foregoing impact limiter designs, there continues to be a need for improvements in impact limiters in order to protect the public from the catastrophic effects of an occurrence wherein the transportation casks and containment vessel are breached, and radiation from the spent nuclear fuel escapes. In addition, there continues to be a need for maximizing the amount of fuel that can be transported by a transportation cask and containment vessel so that the number of trips to transport a given amount of fuel can be reduced, thus minimizing the overall risk to the public.